Antioxidants for mineral oil lubricants and compositions containing the same



Patented June 13, 1950 ANTIOXIDAN'IS FOR MINERAL OIL LUBRI- CANTS AND COMPOSITIONS CONTAINING THE SAME vania v No Drawing. Application December 21, 1948, Serial No. 66,585

14 Claims. (01. 252-50) This invention relates to antioxidants for mineral oil lubricants and compositions containing the same, and more particularly, it relates to addition agents for mineral oil lubricants which inhibit the oxidative deterioration of said lubricants.

In the lubrication of internal combustion engines of all types, particularly when severe operating conditions are encountered, plain mineral lubricating oils often prove unsatisfactory in service because of the oxidative deterioration of the oil, with the attendant deposition on the engine surfaces of varnish, gum or sludge. Furthermore, many lubricating oil compositions which may be highly satisfactory for the lubrication of other mechanisms have been found wholly unsuitable for use as turbine oils.

The formation of varnishes, gums and sludges on engine surfaces is due at least in part to oxidation effects on mineral lubricating oils. In turbine oils the problem of oxidation is further aggravated, because in normal use turbine oils rapidly become contaminated with water.

It has heretofore been proposed to employ as oxidation inhibitors diamino diaryl alkanes, such as tetramethyldiamino diphenyl methane. However, the antioxidant potency of such compounds has not been entirely satisfactory because it is relatively low.

It is an object of this invention, therefore, to provide an addition agent for mineral oil lubricants which will inhibit the oxidative deterioration of such lubricants.

It is a further object of this invention to provide improved mineral oil lubricant compositions which are remarkably stable against oxidation under service conditions.

These and other objects are accomplished by the present invention wherein an addition agent for mineral oil lubricants is prepared by condensing a reactant mixture consisting of N-dimethylaniline and formaldehyde in the presence of an activated clay catalyst, and recovering the condensation product. The condensation product so obtained is a light-colored product which, when added to mineral oil lubricants, confers a remarkable stability against deterioration by oxidation. Such condensation products and the mineral oil lubricant compositions containing them are believed to be novel and are considered parts of our invention. Contrary to what may be expected from the nature of the reactants, we do not obtain highly-condensed, insoluble resinous products. On the contrary, when the above reactants are condensed in accordance with our invention, there are obtained light-colored condensation products which are non-resinous and which are readily soluble in mineral oils.

In performing the condensation, the reactants are mixed and heated to a maximum tem- Derature of 350 F. We have found that if the temperature of 350 F. is exceeded to any substantial extent, the condensation product formed tends to be resinous and insoluble. The preferred temperature for the condensation ranges from 150 to 300 F.

The proportions of the reactants relative to each other may vary over a fairly wide range. As a lower limit, the mol ratio of formaldehyde to N-dimethylaniline should not be less than 0.5:1. However, it is preferred to employ larger amounts of formaldehyde relative to the N-dimethylaniline, since more potent antioxidants are obtained thereby. Accordingly, the mol ratio of formaldghyde to N-dimethylaniline may be as high as 1 :1.

Ordinarily, it is preferred to use from 5 to per cent by weight of the activated clay catalyst, based on the total weight of the reactants. However, smaller amounts, as low as 1 per cent by weight, and larger amounts, as high as 20 per cent by weight, may also be employed; but larger amounts than about 10 per cent by weight are ordinarily not necessary.

In lieu of formaldehyde, any formaldehydeyielding compound, such as paraformaldehyde, dioxymethylene and trioxymethylene may be employed. In such case, the amount of formaldehyde-yielding compound used is based on the equivalent number of mols of formaldehyde yielded within the range of proportions of formaldehyde set forth hereinabove. Accordingly, as used in the appended claims, the term "formaldehyde is intended to include formaldehydeyielding compounds as well as formaldehyde itself.

Various activated clays may be employed in accordance with our invention. Such materials are well known in the art and comprise a natural clay, such as bentonite, fullers earth, fioridin and smectite, which has been acid treated in order to activate the clay. These materials are described in U. S. Patent 1,898,165, for example.

In preparing our new addition agents, the reactants and catalyst are placed into a reaction vessel which is then closed and the mixture heated with agitation until all of the formaldehyde or formaldehyde-yielding compound has been consumed. At this time, the water which is formed as a result of the condensation is removed,

preferably under vacuum, and the dehydrated condensation product is then filtered to remove the activated clay catalyst. In some instances, it is desirable to prepare our new addition agent in a concentrate in a mineral lubricating oil which may then be diluted with additional oil to the concentration desired in the final lubricating compositions. In such instances, the mineral lubricating oil may be added in a suitable amount, say in a weight equal to the weight of reactants, to the reaction mixture in thereaction vessel, and the condensation product obtained will then be a concentrated solution of the addition agent in the mineral lubricating oil.

The condensation products obtained in accordance with our invention are liquids or crystalline solids. composition of the condensation products is unknown, the reactants enter into a unitary product. The exact manner in which the catalyst infinances the reaction is unknown. However, re-

gardless of any theory involved, the use of an I activated clay catalyst i an essential feature of our invention, since if the catalyst is omitted, black, insoluble, resinous condensation products may be obtained. The catalyst in some manner also affects the antioxidant potency of the resulting condensation products. Thus, even when the N-dimethylaniline and formaldehyde are used in such molar proportions as to lead to the assumption that tetramethyldiamino diphenyl methane would be obtained, i. e., 2 mols of N- dimethylaniline and 1 mol of formaldehyde, the condensation product obtained by condensing 2 mols of N-dimethylaniline and 1 mol of formaldehyde in the presence of an activated clay catalyst has suchagreater antioxidant potency than tetramethyldiamino diphenyl methane, that the conclusion is unmistakable that the latter compound is not obtained. Thus, in U. S. Patent 2,452,320, column 4, line 1 et seq.. 0.1 per cent of tetramethyldiamino diphenyl methane. when added to a solvent-refined, acid treated and filtered reference lubricating oil having a viscosity range of 485-515 Saybolt Universal at 100 F., increased the antioxidant potency of the reference 011 from 65-72 hours only to 174-200 hours. When 0.1 per cent of a condensation product of 2 mols of N-dimethylaniline and one mol of formaldehyde prepared in accordance with our invention was added to a similar reference 011, the antioxidant potency was increased to 550 hours, at least 2% times over that obtained with tetramethyldiamino diphenyl methane.

The following examples illustrate the preparation of our new addition agent.

Example I.Into an iron reaction vessel, equipped with means for agitation and a reflux condenser, there were placed 1210 pounds (10 pound mols) of N-dimethylaniline, 420 pounds of formaldehyde in a 37 per cent by weight aqueous solution (5 mols of anhydrous formaldehyde). and 121 pounds of Filtrol (an activated montmorillonite) as a catalyst. The mixture was agitated and refluxed at 180 F. for 8 hours, and then all water, both that added with the formaldehyde and formed in the reaction, was distilled off by heating at 280 F. and the product dried. The product was then filtered. The product had Example IIJ-Twenty four hundred twenty While the exact nature of the chemical I temperature of 280 F. The product was then filtered. It had the following properties:

Gravity, "API 12.9 Color, NPA 4.0 Neutralization No. 0.52

The condensation products obtained in accordance with the above disclosure from N-dimethylaniline and formaldehyde in the presence of an activated clay catalyst are excellent addition agents for mineral oil lubricants. They are readily soluble in all types of mineral oils, that is, parafllnic, naphthenic or mixed base mineral oils and can be blended with mineral oils in high proportions to form concentrated solutions thereof, which may then be diluted down to the proportions desired in the final mineral oil lubricant composition. As stated, our new addition agents are remarkably effective in inhibiting the oxidative deterioration of mineral oil lubricant compositions. For this purpose small amounts of our new addition agents are generally sufficient. For example. our addition agents may be added to mineral lubricating oils in minor amounts, say from 0.001 to 1 per cent by weight on the mineral oil. sufllcient to inhibit the oxidative deterioration of the oil. Larger amounts of our new addition agents may be used if desired but it is ordinarily unnecessary to do so.

The following examples illustrate the remarkable antioxidant effects of our new addition agents. In the following examples, the base oil and the same 011 blended with our new addition agents are subjected to a standard oxidation test which measures the stability of the oils to oxidation. The oxidation test referred to is a standard test designated ASTM D943-47T. Briefly, the test comprises subjecting the oil sample to oxygen atatemperature of C. (203 F.) in the presence of water and an iron-copper catalyst, and determining the time required to build up a neutralization number of 2. The fiow of oxygen is maintained at 3 liters per hour. The remarkably effective stability to oxidation of mineral oil lubricant compositions containing our new addition agents is illustrated by the results shown in the following examples.

Example IIL-An improved steam turbine oil was prepared by adding 0.5 per cent by weight of the addition agent prepared in accordance with Example I to a turbine 011 base. A comparison of the base oil and the base oil blended with the antioxidant showed the following result:

Example IV.--To a refined motor oil base, there was added 0.5 per cent by weight of the addition agent prepared in accordance with Exampl I. A comparison of the base oil and improved oil follows:

Example V.An improved steam turbine oil was prepared by adding 0.5 per cent by weight of the addition agent prepared in accordance with Example II to a turbine 011 base. A comparison of the base oil and the improved oil showed:

Base Improved on on Gravity, API 28.5 28.4 0x6dation TestirAsTM D943-47T 203 F., a L.

iin xi dizedflirs 180 4,350 Neutralization N o 2. 0 2.0

Example VI.An improved motor oil was prepared by adding 0.5 per cent by weight of the addition agent prepared in accordance with Example II to a motor oil which has been highly refined by an aluminum chloride treatment. A comparison of the base oil and the improved oil showed:

Base Improved on on Gravity, API 29.1 29.6 Viscosity, SUV: 100 F.-- 380 378 Color, I 2.5 2.5 Oxidation Test, ASTM pea-411' 203 F., a L.,

Oxygen per Hr.

Time Oxidized, Hrs 210 3,575 Neutralization No 2. 0 2. 0

The above examples show the remarkable oxidation stability imparted to mineral oil lubricant compositions by the use of our new addition agents. Mineral oil lubricant compositions containing our new addition agents are therefore eminently suited for use where the operating conditions are extremely severe, as in Diesel, tank and truck engines, and in the lubrication of steam turbines.

The remarkable effects of our new addition agents cannot be readily accounted for and cannot be predicted from the nature of the reactants. Thus, condensation products prepared from other functionally similar compounds have been found to be either prooxidant or to shOW no antioxidant efl'ects whatsoever. For example, we have prepared a condensation product similar to our new addition agent by substituting other amines such as xylidine and N-diethylaniline for N-dimethylaniline. The resulting condensation products were found to be entirely unsuitable for inhibiting the oxidative deterioration of mineral oil lubricant compositions. It is surprising that the substitution of an isomer, xylidine, or the next higher homologue, N-diethylaniline, for the N-dimethylaniline produces condensation products which are not antioxidants for mineral lubricating oils. Thus, the addition to a mineral lubricating oil of 0.5 per cent of a condensation product of N-diethylaniline and formaldehyde (prepared exactly as the condensation product of N-dimethylaniline a and formaldehyde of this invention) fails to improve the oxidation stability of the lubricating oil. Similarly, the substitution of xylidine for the N- dimethylaniline yields an unsatisfactory product.

It is obvious, therefore, that the type of amine used to condense with the formaldehyde is a highly critical feature of this invention. It is also obvious that it is impossible to predict which amine will yield a satisfactory antioxidant, the selection of the amine being purely empirical. Although N-diethylaniline does not produce a satisfactory antioxidant, we have found that the N- diethyltoluidines will produce excellent antioxidants. This is described and claimed in our copending application Serial No. 66,586, filed of even date herewith. Furthermore, mixtures of the N- diethyltoluidines and of N-dimethylaniline may be condensed with formaldehyde in the presence of an activated clay to produce excellent antioxidants. This is described and claimed in our copending application Serial No. 66,587, filed of even date herewith. Finally, even though N-diethylaniline when condensed alone with formaldehyde does not yield a satisfactory antioxidant, when mixtures of N-diethylaniline and N-dimethylaniline are condensed with formaldehyde in the presence of an activated clay, good antioxidants are obtained. This is described and claimed in our copending application Serial No. 66,588, filed of even date herewith.

While we have shown in the examples the preparation of compounded lubricating oils, our invention is not limited thereto but comprises all mineral oil lubricant compositions containing our new addition agents, such as greases and the like. If desired, other known addition agents. may be incorporated into the lubricant compositions prepared in accordance with our invention. For example, pour point depressants, extreme-pressure agents, viscosity index improvers and the like may be added.

Resort may be had to such modifications and variations as fall within the spirit of the invention and the scope of theappended claims.

We claim:

1. The process of preparing an addition agent for mineral oil lubricants which comprises heating a reactant mixture consisting of N-dimethylaniline and formaldehyde in the presence of an activated clay catalyst at a temperature not in excess of 350 F. to condense together the two reactants, and recovering the condensation product, the mol ratio of formaldehyde to N-dimethylaniline ranging from 0.5:1 to 10:1.

2. The process of preparing an addition agent for mineral oil lubricants which comprises heating a reactant mixture consisting of N-dimethylaniline and formaldehyde in the presence of 5 to '10 per cent by weight on the total reactants of an activated clay catalyst at a temperature of from 150 to 300 F. to condense together the two reactants, and recovering the condensation product, the mol ratio of formaldehyde to N-diing a reactant mixture consisting of 2 mols of N-dimethylaniline 1 mol of formaldehyde in the presence of-about 5 to per cent by weight on the total reactants of an activated clay catalyst at a temperature of from 150 to 300 1"" to condense together the two reactants, and recovering the condensation product.

5. The process of preparing an addition agent for mineral oil lubricants which comprises heating a reactant mixture consisting of 1 mol of N-dimethylaniline and 1 mol of formaldehyde in the presence of about5 to 10 per cent by weight on the total reactants of an activated clay catalyst at a temperature of from 150 to 300 1''. to condense together the two reactants, and recovering the condensation product. I

6. A non-resinous condensation product of N- dimethylaniline and formaldehyde in a mol ratio of formaldehyde to N-dimethylaniline ranging from 0.5:1 to 10:1, said product being obtained by the process of claim 1.

7. A non-resinous condensation product of 2 mols of N-dimethylaniline and 1 mol of formaldehyde; said product being obtained by the process of claim 4.

8. A non-resinous condensation product of 1 mol of N-dimethylaniline and 1 mol of formaldehyde, said product being obtained by the process of claim 5.

9. A lubricant composition comprising a major amount of a mineral lubricating oil, and a minor amount, sufllcient to inhibit the oxidative deterioration of said oil of a non-resinous condensation product of N-dimethylaniline and formaldehyde in a mol ratio of formaldehyde to N-dimethylanine ranging from 0.5:1 to 10:1, said product being obtained by the process of claim 1.

10. A lubricant composition comprising a major amount of a mineral lubricating oil, and a minor amount, from 0.001 to 1.0 per cent by weight of said oil, of a non-resinous condensation prodnot of N-dimethylaniline and formaldehyde in a mol ratio of formaldehyde to N-dimethylaniline ranging from 0.5:1 to 10:1, said product being obtained by the process of claim 1.

11. A lubricant composition comprising a major amount of a mineral lubricating oil, and a minor amount, sumcicnt to inhibit the oxidative deterioration of said oil of a non-resinous condensation product of 2 mols of N-dimethylaniline and 1 mol of formaldehyde, said product being obtained by the process of claim 4.

12. A lubricant composition comprising a major REFERENCES CITED The following references are of record in the file ofthis patent:

- UNITED STATES PATENTS Number Name Date 1,584,473 Regal May 11, 1926 1,803,331 Kladivko May 5. 1931 1,873,790 Vacher Aug. 23, 1932 1,954,484 Mattison Apr. 10, 1934 2,223,411 Puller et al. Dec. 3, 1940 2,454,890 Smith et al. Nov. 30, 1948 FORETGN PATENTS Number Country Date 12,021 Amtralia reb. 29. 1928 

1. THE PROCESS OF PREPARING AN ADDITION AGENT FOR MINERAL OIL LUBRICANTS WHICH COMPRISES HEATING REACTANT MIXTURE CONSISTING OF N-DIMETHYLANILINE AND FORMALDEHYDE IN THE PRESENCE OF AN ACTIVATED CLAY CATALYST AT A TEMPERATURE NOT IN EXCESS OF 350*F. TO CONDENSE TOGETHER THE TWO REACTANTS, AND RECOVERING THE CONDENSATION PRODUCT, THE MOL RATIO OF FORMALDEHYDE TO N-DIMETHYLANILINE RANGING FROM 0.5:1 TO 10:1.
 10. A LUBRICANT COMPOSITION COMPRISING A MAJOR AMOUNT OF A MINERAL LUBRICATING OIL, AND A MINOR AMOUNT, FROM 0.001 TO 1.0 PER CENT BY WEIGHT OF SAID OIL, OF A NON-RESINOUS CONDENSATION PRODUCT OF N-DIMETHYLANILINE AND FORMALDEHYDE IN A MOL RATIO OF FORMALDEHYDE TO N-DIMETHYANILINE RANGING FROM 0.5:1 TO 10:1, SAID PRODUCT BEING OBTAINED BY THE PROCESS OF CLAIM
 1. 